This paper is one of a series published by Volunteers in Technical Assistance to provide an introduction to specific state-of-the-art technologies of interest to people in developing countries. Ultimately, to be effective a sanitation system must reach the whole community, in its physical extent and in the tendency of people to take advantage of it. The community can provide the most modern water and waste disposal systems available; but if large segments of the people are not served by these systems, a major breakdown in the sanitation level is likely to occur with the accompanying potential for the spread of disease and infection.